An extracellular Ca.sup.2+ -sensing receptor (CaR) has been cloned from both bovine and human parathyroids, and there is evidence indicating that this receptor plays a key role in regulating extracellular calcium homeostasis by controlling PTH secretion (Pollak, et al., Cell 75:1297-1303 (1993); Pollak, et al., Nature Genet. 8:303-307 (1994); Pollak, et al., J. Clin. Invest. 93:1108-1112 (1994)). The isolation and identification of the avian counterpart of this receptor and of polynucleotides encoding the receptor should aid in the development of methods for regulating serum calcium levels in chickens and related species. By increasing serum calcium in such animals, it is expected that more rapid growth should be obtainable due to an increased rate of bone deposition and that eggs of higher quality should be produced.